There is a paucity of literature on heteroatom removal-directed/enhancing aqueous CO hydrogenation of refractory heteroatom containing aromatic ring structures such as those typically found in coals and similar organic resources in the absence of certain reaction inducing factors such as transition metal catalysts. Stenberg, et al. J. Am. Chem. Soc. 43, 2991 (1978) teaches that quinoline can be hydrogenated using supercritical water and CO at 425.degree. C., optionally in the presence of Na.sub.2 CO.sub.3, but Stenberg's product analysis specifically shows that nitrogen was not removed. Appell, et al. Prepr.-Pap. ACS Div. Fuel Chem. 12, 220(1968) and Appell, et al., Prepr.-Pap. ACS Div. Fuel Chem. 13, 39 (1969) teach that a complex mix of products may be produced by treating a coal with CO and water in a conversion process at a temperature of below about 425.degree. C. British Patent 1,461,280 to Bull, et al., suggests that sulfur can be removed under aqueous CO conditions in the presence of a hydrogenated aromatic solvent. Given the known stability of heteroatom containing biaryl linkages, one skilled in the art would not expect that the product mix would have been the result of dearomatization and cleavage of structures containing the biaryl bond.
To date only one publication, Siskin, Tetrahedron Letters 34, 4739 (1993), discloses hydrogenation along with heteroatom removal under aqueous CO reaction conditions, and that reference shows only that a monoaromatic heteroatom containing ring (i.e., pyridine) was reactive. No compounds containing biaryl linkages were tested nor did the reference suggest that they would be reactive.
There has been a measure of success, in liquid and supercritical water based systems, in reacting molecules containing certain linkages typically found in coal, such as ethers, sulfides and amines. See, e.g., Siskin in Science Vol. 254 p. 231-237, (11 Oct. 1991 ) which teaches that liquid water may be used under certain conditions. M. T. Klein, Fuel 64, 635 (1985); Industrial Eng. Chem. Products Res. & Devel. 24, 300 (1985); Fuel Science and Technol. 6, 633 (1988), teaches ethers, amines and sulfides may be cleaved in supercritical water. Hydrogenation and removal of nitrogen and sulfur from heteroaromatic rings is not taught or suggested. In addition, the molecules disclosed by Siskin and Klein contain linkages that are known to be much more reactive than those on which Applicant's process operates. Thus, one skilled in the art would not consider these disclosures to be relevant teachings.
Certain literature does describe processes that operate on organic resources, such as coal. For example, in U.S. Pat. No. 3,988,238 to McCollum, supercritical water may be used to crack and remove nitrogen and sulfur from coals. However, McCollum required the presence of a sulfur resistant transition metal catalyst and did not teach hydrogenation of the resource, given the absence of a reducing agent such as CO in the system. McCollum, U.S. Pat. No. 4,005,005 also suggests that tar sands may be cracked, and desulfurized using a dense fluid extraction. However, the patent specifically teaches that a reducing environment is not an element of the process. U.S. Pat. No. 5,269,947 to Baskis discloses a two zone water based thermal depolymerization process for process materials such as coal, with removal of some sulfur, but only by virtue of the inclusion of a separate catalytic sulfur removing process unit. Similarly Delbianco, U.S. Pat. No. 4,968,414 discloses a two stage process for coal liquefaction in the presence of CO and an alkaline carbonate or hydroxide. However, Applicants process operates without the required temperature staging of Delbianco.
Some processes do exist in which a reducing environment, specifically CO is disclosed. For example U.S. Pat. No. 5,151,173 to Vaughn discloses CO pressures of from about 800 to about 4500 psi, in conjunction with liquid water at a temperature of less than 700.degree. F. for coal depolymerization and hydrogenation. The process, however, specifically teaches that heteroatom content reduction from coal does not occur (see e.g., Table 6 of U.S. Pat. No. 5,151,173). This is consistent with that which one skilled in the art would expect, given the highly aromatic content of coals. In addition, the work by Appell described previously, even though carried out at higher temperatures also did not teach that heteroatom removal may be accomplished.
Canadian Patent 2,000,251 to Berkowitz discloses a supercritical water CO extraction upgrading process for generating liquids from tar sands. However, there is no teaching nor suggestion of N or S removal, which is understandable given the nature (high H to C ratio) of the resource on which the process operates. Upgrading in this reference means making liquid products of an unspecified nature.
Finally, Cummins, Energy Commun., 6,117 (1980), has reported the use of a CO-steam process to convert or crack oil shale kerogens to liquid products. However, he also reported that hydrogenation did not produce any nitrogen or sulfur removal within the temperature range of 300.degree.-450.degree. C., and specifically required a constant CO pressure of only 1.4 MPa (200 psig).